<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <script>
        window.onbeforeunload = function() {
            return "该网页正在运行重要内容，关闭网页可能会损坏你的计算机，是否真的要关闭？";
        }
    </script>
</body>

</html>